Disc reproducing system

ABSTRACT

A disc playback system according to this invention, as shown in FIG.  1 , comprises a pickup  1  for reading information from an information disc  2  on which data are recorded at a constant linear velocity, a disc motor 16 for rotating the information disc  2 , a digital signal processing means  7  for digitizing data according to the playback format of the information disc  2 , an interface means  19  for transmitting the digitized data to an external device and a buffer memory  18  for temporarily containing the data, and further includes a means for detecting the linear velocity and track pitch of the information disc  2  to decide the reference value for the velocity control of the disc motor  16  on the basis of the detected values of the linear velocity and track pitch and the value of the maximum radius of the data record area. According to the so-constructed disc playback system, the maximum playback velocity of the system can be obtained even in the case of discs having different track pitches.

TECHNICAL FIELD

The present invention relates to a disc playback system to be used inCD-ROM playback apparatus or the like and, more particularly, to a discplayback system for controlling the disc rotation velocity.

BACKGROUND ART

As common methods for controlling the disc rpm in conventional discplayback Systems, there are CAV (Constant Angular velocity) controlunder which the angular velocity is constant, CLV (Constant Linearvelocity) control under which the linear velocity is constant, andfurther PCAV control in which the CAV control and the CLV control arecombined. Since the CLV control among these-requires frequentacceleration or deceleration of the spindle motor at a time ofaccessing, there are various problems, such as delay of the access time,increases in the consumed power, and heat generation. Accordingly, withthe recent speeding-up of the CD-ROM apparatus, the CAV control or thePCAV control has been commonly used at the time of playback of discs onwhich data are recorded by the CLV method.

Under the CAV control, for example in the case of CD, the error ofapproximately 1.2˜1.4 m/s is tolerated in the linear velocity, but thevalue of the linear velocity is not recorded on the medium. Thus, somemethods for measuring the linear velocity of an information disccontaining data recorded by the CLV method, at the time of loading ofthe disc are suggested.

For example, in a disc playback apparatus disclosed in Japanese ExaminedPatent Application No.Hei-5-50074, the linear velocity of the medium isobtained by forcefully transporting the pickup from the program startposition of the information disc toward the inner radius by one trackand counting the playback frame synchronization signal until the programstart position is detected again. Under the CAV control, severalpercentages of the rotation velocity due to the error in the linearvelocity is finely adjusted and the control of the rotation velocity ofthe disc is performed at a constant velocity. When the rpm is constant(CAV) at this time, because the linear velocity is higher at the outerradium of the disc, the playback velocity of data becomes higher.However, the maximum playback velocity conforming to the performance ofthe data playback circuitry has already been determined and thus therotation velocity of the disc should be set so as not to exceed thismaximum playback velocity, while the quantity of data recorded on thedisc varies with discs. Therefore, following control means are suggestedto solve this problem.

In the disc playback system disclosed in Japanese Published PatentApplication No. Hei.7-312011, a method for calculating the outermostcircumference position of a disc from TOC (Table of Contents)information of a CD-ROM and controlling the rotation velocity of thedisc so as to obtain the maximum velocity in the system at the outermostcircumference position containing recorded data is suggested.

In another disc playback system, a method for storing the outermostcircumference position which has already been accessed, and controllingthe rotation velocity of the disc so as to obtain the maximum velocityin the system at the stored address is also suggested in view of thefact that there are few cases where all data on the disc are used.

As described above, to calculate the maximum velocity, in the case ofCD, the standards tolerate the error of approximately 1.2˜1.4 m/s in thelinear velocity. In addition to this, as for the space between tracks(hereinafter referred to as track pitch), its standard value is 1.6 μmwhile the standards accept the error in the range of 1.5˜1.7 μm. Forreference purposes, in the case of CD-ROM, the standard value of thetrack pitch is 1.6 μm. Therefore, by using this value, the outermostcircumference radius for obtaining the maximum velocity in the system iscalculated from the address information and linear velocity of the disc.

However, in this conventional disc playback system, in the case of adisc having a smaller track pitch than the standard value, the actualplayback velocity at a radius of the outermost circumference position islower than the maximum velocity in the system. On the other hand, in thecase of a disc having a larger track pitch than the standard value, theactual playback velocity at a radius of the outermost circumferenceposition is higher than the maximum velocity of the system. Thus, in thenormal disc playback system, the playback velocity at the outermostcircumference position should be decided using the permissible maximumtrack pitch, but when a disc having a smaller track pitch than thepermissible maximum value is played back in this case, the maximumplayback velocity of the system cannot be realized.

To be more specific, the track pitch of a CD-ROM has a range of 1.5˜1.7μm according to the standards. However, because there are discs out ofthe standards in practice, the target reading velocity cannot berealized or the reading velocity exceeding the processing capability ofthe system is obtained in the case of a disc having a value which isquite different from the standard track pitch (1.6 μm).

The present invention is made to solve the above-mentioned problems, andhas its object to provide a disc playback system in which the maximumplayback velocity of the system can be obtained even in the case of thedisc having a different track pitch.

DISCLOSURE OF THE INVENTION

To solve these problems, a disc playback system of Claim 1 of thepresent invention comprises: a pickup for reading first information datarecorded on an information disc on which data are recorded at a constantlinear velocity, from the information disc; a disc motor for rotatingthe information disc; a digital signal processing circuit for digitizingthe first information data according to a playback format of theinformation disc; an interface control circuit for transmitting secondinformation data which are the data digitized by the digital signalprocessing circuit, to an external device; a buffer memory fortemporarily containing the second information data which are requestedby the external device via the interface control circuit; a linearvelocity detection means for detecting a linear velocity of theinformation disc; and a track pitch detection means for detecting atrack pitch of the information disc, and this disc playback systemdecides a reference value for controlling a velocity of the disc motor,on the basis of the linear velocity detected by the linear velocitydetection means, the track pitch detected by the track pitch detectionmeans, and a value of a maximum radius of a record area of data whichare recorded on the information disc. Therefore, the accurate values ofthe linear velocity and track pitch can be obtained for each disc.Accordingly, the accurate rotation velocity of the disc motor can becalculated from the values of the linear velocity and track pitch andthe address value of the maximum radius of the record area of data whichare recorded on the information disc, whereby the high-speed search orhigh-speed reading can be performed adaptively according to theoutermost circumference radius of the data record area.

According to a disc playback system of Claim 2 of the present invention,in the disc playback system of Claim 1, the track pitch detection meanscomprises a motion distance detection means for detecting a motiondistance of the pickup, and when the information disc is loaded, themotion distance detection means calculates the number of tracks whichhave been passed by the pickup while the pickup is moving on the datarecord area on the information disc for a prescribed time period or by aprescribed distance, thereby detecting the track pitch of theinformation disc. Therefore, the accurate value of the track pitch canbe obtained fur each disc. In addition, the accurate rotation velocityof the disc motor can be calculated from the value of the track pitch,the value of the linear velocity, and the address value of the maximumradius of the record area of data which are recorded on the informationdisc, whereby the high-speed search or high-speed reading can beperformed adaptively according to the outermost circumference radius ofthe data record area.

A disc playback system according to Claim 3 of the present inventioncomprises: a pickup for reading first information data recorded on aninformation disc on which data are recorded at a constant linearvelocity, from the information disc; a disc motor for rotating theinformation disc; a digital signal processing circuit for digitizing thefirst information data according to a playback format of the informationdisc; an interface control circuit for transmitting second informationdata as data which have been digitized by the digital signal processingcircuit, to an external device; a buffer memory for temporarilycontaining the second information data which are requested by theexternal device via the interface control circuit; a linear velocitydetection means for detecting a linear velocity of the information disc;and a playback velocity detection means for detecting a playbackvelocity of the information disc during playback of the information, andthis disc playback system previously decides an initial value of areference value for controlling a velocity of the disc motor on thebasis of the linear velocity detected by the linear velocity detectionmeans, a standard maximum value of a track pitch of the informationdisc, and a value of the maximum radius of a record area of data whichare recorded on the information disc, when data are read from theinformation disc, sets again the reference value for controlling thevelocity of the disc motor adaptively on the basis of the playbackvelocity of the information disc during playback, which is detected bythe playback velocity detection means, the linear velocity detected bythe linear velocity detection means, and a value of an address at whichthe playback is being performed, and decides the reference value forcontrolling the velocity of the disc motor. Therefore, no specific meansfor detecting the track pitch is required, and the value of the maximumradius of a record area of data which are recorded on the informationdisc can be calculated less expensively and more accurately, regardlessof the values of the linear velocity and track pitch of the informationdisc. In addition, even when the previously measured linear velocity ofthe information disc has an error, the high-speed search or high-speedreading can be performed adaptively according to the outermostcircumference radius of the data record area.

According to a disc playback system of Claim 4 of the present invention,in the disc playback system of Claim 3, the reference value forcontrolling the velocity of the disc motor is obtained when thereference value for the velocity control is set again, by making acompensation by multiplying the initial value of the motor velocitycontrol reference value, by a compensation coefficient corresponding toa ratio between a radius position at which the information disc is beingplayed back or an address value thereof, and the value of the maximumradius of the data record area or an address value thereof. Therefore,the maximum radius of the data record area on the information disc canbe calculated more accurately, by making a compensation by multiplying acompensation coefficient corresponding to the radius position where theplayback is being performed or its address value, regardless of theradius position where the information disc is being played back or itsaddress value, or the values of the linear velocity and track pitch ofthe disc, as well as even when the previously measured linear velocityof the disc has an error, the high-speed search or high-speed readingcan be performed adaptively according to the outermost circumferenceradius of the data record area.

According to a disc playback system of Claim 5 of the present invention,the disc playback system of any of Claims 1, 3 and 4 extracts addressinformation concerning the information disc which is stored in a discstart position, from the first information data, and uses a value of aradius in a maximum circumference position obtained by the addressinformation, as the value of the maximum radius of the record area ofdata which are recorded on the information disc. Therefore, the maximumradius of the data record area on the information disc can be calculatedmore accurately, regardless of the values of the linear velocity andtrack pitch of the information disc, whereby the high-speed search orhigh-speed reading can be performed adaptively according to the datastorage capacity of the disc.

According to a disc playback system of Claim 6 of the present invention,the disc playback system of any of Claims 1, 3 and 4 comprises a storagemeans for containing address information of the outermost circumferenceamong already read address information on the information disc, and usesa radius of an address position of the outermost circumference, readfrom the storage means, as the value of the maximum radius of the recordarea of data which are recorded on the information disc. Therefore, theoutermost circumference radius of the addresses which have ever beenaccessed on the information disc can be calculated more accurately,regardless of the values of the linear velocity and track pitch of theinformation disc, whereby the high-speed search or high-speed readingcan be performed adaptively according to the address of the outermostcircumference radius which has ever been accessed on the informationdisc.

According to a disc playback system of Claim 7 of the present invention,in the disc playback system of any of Claims 1 to 6, the disc motorcomprises: a CAV (Constant Angular Velocity) control circuit forrotating the information disc at a constant angular velocity. Therefore,the maximum radius of the data record area on the disc can be calculatedmore accurately, regardless of the values of the linear velocity andtrack pitch of the disc, whereby the high-speed search or high-speedreading can be performed adaptively according to the outermostcircumference radius of the data record area.

According to a disc playback system of Claim 8 of the present invention,in the disc playback system of any of Claims 1 to 6, the disc motorcomprises; a CLV (Constant Linear Velocity) control circuit for rotatingthe information disc at a constant linear velocity, and a variable clockgeneration circuit which can vary a comparison clock supplied to the CLVcontrol circuit on the basis of the reference value for controlling thevelocity of the disc motor. Therefore, the maximum radius of the datarecord area on the information disc can be calculated more accurately,regardless of the value of the track pitch, whereby the high-speedsearch or high-speed reading can be performed adaptively according tothe outermost circumference radius of the data record area.

According to a disc playback system of Claim 9 of the present invention,in the disc playback system of any of Claims 1 to 6, the disc motorcomprises: a first rotation control means for rotating the informationdisc at a constant angular velocity, a second rotation control means forrotating the information disc at a constant linear velocity, and aswitch circuit for switching the first rotation control means and thesecond rotation control means. Therefore, the maximum radius of the datarecord area on the information disc can be calculated more accurately,regardless of the value of the track pitch, whereby the high-speedsearch or high-speed reading can be performed adaptively according tothe outermost circumference radius of the data record area.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a CAV playback system accordingto a first embodiment of the present intention.

FIG. 2 is a block diagram illustrating a disc playback system which isapplied to a CAV playback system for CD-ROM according to second andfourth embodiments of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

Hereinafter, the first embodiment of the present invention correspondingto Claims 1 and 2 will be described with reference to FIG. 1.

FIG. 1 is a block diagram illustrating a CAV playback system accordingto the first embodiment.

Reference numeral 2 denotes an information disc on which data arerecorded at a constant linear velocity. The information disc 2 hasprescribed ranges of tolerances as to the linear velocity, the trackpitch, and the innermost radius of the data record area in which dataare recorded on the information disc 2. Numeral 1 denotes a pickup forreading information from the information disc 2, such as an opticalpickup and a magnetic head. Numeral 3 denotes an amplifier circuit,which amplifies a signal read by the pickup 1 so as to have anappropriate amplitude. Numeral 16 denotes a disc motor, which rotatesthe information disc 2 at a predetermined velocity. Numeral 4 denotes aservo control circuit, which controls the pickup 1 to be in anappropriate position on a target track. Numeral 5 denotes an A/Dconverter circuit, which binarizes the signal transmitted from theamplifier circuit 3 and generates a PLL (Phase Locked Loop) clock whichis synchronized with the binarized signal. Numeral 7 denotes a digitalsignal processing circuit, which processes a supplied digital signal inaccordance with a playback format of data, in synchronization with thePLL clock. Numeral 18 denotes a buffer memory, which temporarilycontains the signal processed by the digital signal processing circuit7. Numeral 19 denotes an interface control circuit, which transmits thedata stored in the buffer memory 18 to an external device. Numeral 20denotes a disc motor control circuit, which rotates the disc motor 16 ata suitable velocity in accordance with an instruction from a maximumvelocity definition circuit 22. Numeral 6 denotes a system controller,which controls the servo control circuit 4 and the interface controlcircuit 19.

The operation in the so-constructed disc playback system for controllingthe rotation velocity of the information disc 2 is described withreference to FIG. 1.

When the information disc 2 is loaded into the disc playback system, thedisc motor 16 rotates the information disc 2 at a prescribed velocity inthe disc playback system. In order to control the rotation velocity ofthe disc motor 16, it is required to obtain values of the linearvelocity and track pitch of the information disc 2.

Initially, the value of the linear velocity of the information disc 2 ismeasured for example by the following method. In cases where the pickup1 has a means for detecting the range of motion of the information disc2, when the information disc 2 is loaded into the apparatus, the pickup1 is transported from the program start position of the information disc2 toward the inner radius of the track. Then, the pickup 1 counts aplayback clock for the signal processing until it detects the programstart position again, whereby the linear velocity can be measured.

Next, the servo control circuit 4 detects the range of motion of thepickup 1 to obtain the value of the track pitch. For example, in caseswhere an encoder system or the like is included as a means for detectingthe track pitch, when the information disc 2 is loaded, the informationdisc 2 is moved by a prescribed range or for a prescribed time periodand the pickup 1 measures the number of tracks which have been passedduring that time, whereby the track pitch can be measured.

Therefore, the rotation velocity of the disc motor 16 can be obtainedfrom the measured values of the linear velocity and track pitch, and theaddress value of the maximum radius of the data record area in which thedata are recorded on the information disc 2.

As described above, according to the disc playback system of the firstembodiment, since the means for detecting the linear velocity and thetrack pitch of the information disc 2 are provided, the correct valuesof the linear velocity and the track pitch can be obtained for eachdisc. Therefore, the accurate rotation velocity of the disc motor 16 canbe calculated from the values of the linear velocity and track pitch,and the address value of the maximum radius of the data record area inwhich data are recorded on the information disc 2, whereby thehigh-speed search or high-speed reading can be adaptively performed,according to the outermost circumference radius of the-data record area.

Embodiment 2

Hereinafter, the second embodiment of the present inventioncorresponding to Claims 3 and 4 will be described with reference to FIG.2.

FIG. 2 is a block diagram illustrating a disc playback system which isapplied to a CAV playback system for CD-ROM according to the secondembodiment. When the pickup has no means for detecting the range ofmotion of the information disc, the rotation velocity of the disc motorcan be obtained by the following method The same reference numerals asthose in the first embodiment denote the same elements, and thedescriptions thereof are not given here.

In FIG. 2, numeral 21 denotes an optical pickup for reading datarecorded on the information disc 2. Numeral 23 denotes a RF amplifierfor supplying a RF (Radio Frequency) signal read from the optical pickup21. Numeral 24 denotes a focus-tracking control circuit/feed motorcontrol circuit for supplying a focus error signal or tracking errorsignal extracted by the RF amplifier 23. Numeral 25 denotes a levelslice-PLL circuit for supplying the RF signal amplified by the RFamplifier 23. Numeral 26 denotes a CD signal processing circuit forsupplying an EFM signal which is obtained by binarizing the RF signalfrom the level slice-PLL circuit 25. Numeral 11 denotes a CLV motorcontrol circuit for supplying a synchronization signal of a CD and acorrection frame synchronization signal which are detected by the CDsignal processing circuit 26. Numeral 9 denotes a RAM. Numeral 13denotes an interpolation circuit for supplying an audio signal.

Numeral 15 denotes a D/A converter for supplying output data from theinterpolation circuit 13. Numeral 15 a denotes a LPF (low-pass filter)for outputting a playback audio signal from the D/A converter 15 tooutside.

Further, numeral 14 denotes a CD-ROM signal processing circuit forsupplying CD-ROM data. Numeral 10 denotes a clock generator foroutputting a X′TAL (crystal) clock. Numeral 27 denotes a CAV controlcircuit for generating a drive signal for rotating the disc motor 16 ata prescribed-rotation. Numerals 8, 12 and 17 denote selectors.

The operation of the so-constructed disc playback system for controllingthe rotation velocity of the information disc 2 is described withreference to FIG. 2.

In this figure, the RF signal (Radio Frequency) signal read from theinformation disc 2 by the optical pickup 21 is supplied to the RFamplifier 23. The RF amplifier 23 extracts a focus error signal ortracking error signal from the output of the optical pickup 21, thensupplies the extracted signal to the focus-tracking control circuit/feedmotor control circuit 24 as well as supplies an amplified RF signal tothe level slice-PLL circuit 25.

The level slice-PLL circuit 25 can obtain an EFM (Eight to FourteenModulation) signal which is obtained by binarizing the RF signal, andsimultaneously generates a PLL (Phase Locked Loop) clock which issynchronized with the EFM signal to read this EFM signal.

The EFM signal obtained by binarizing the RF signal by the levelslice-PLL circuit 25 is supplied to the CD signal processing circuit 26.In addition, the PLL clock is supplied to the CD signal processingcircuit 26 and the selector 8.

The CD signal processing circuit 26 detects the synchronization signalof the CD using the PLL clock, and performs separation or EFMdemodulation of the data. Then, it extracts only sub code data from thedemodulated data and supplies the sub code data to the system controller6. The synchronization signal of the CD and the correction framesynchronization signal which are detected by the CD signal processingcircuit 26 are supplied to the CLV motor control circuit 11. Further,data are written in the RAM 9 using the PLL clock as other main data.

The data correction process is carried out by reading data from the RAM9 with reference to the clock supplied by the selector 8. At this time,in the case of playback under CAV control, the correction process iscarried out using a playback PLL clock output by the level slice-PLLcircuit 25, and in the (case of playback under CLV control, thecorrection process is carried out using the X′TAL (crystal) clock outputby the clock generator 10. Then, the data which have been subjected tothe correction process are supplied to the interpolation circuit 13 orthe CD-ROM signal processing circuit 14 via the selector 12.

The switching between CAV and CLV is performed in accordance with anaudio/ROM switching instruction signal output by the system controller6. In the case of audio, the CLV playback is carried out, and in thecase of CD-ROM, the CAV playback is carried out.

The switching of the selector 8 is performed in accordance with theaudio/ROM switching instruction signal output by the system controller6. The selector 8 selects the X′TAL clock output by the clock generator10 when the instruction signal indicates audio, and selects the playbackPLL clock output by the level slice-PLL circuit 25 when the instructionsignal indicates a CD-ROM, to be supplied to the CD signal processingcircuit 26.

The switching of the selector 12 is performed in accordance with theaudio/ROM switching instruction signal output by the system controller6. The selector 12 supplies data to the interpolation circuit 13 whenthe instruction signal indicates audio, and supplies data to the CO-ROMsignal processing circuit 14 when the signal indicates a CD-ROM.

Only when an error flag is included in the data, the interpolationcircuit 13 performs the interpolation of the data, and supplies theoutput to the D/A converter 15. The D/A converter 15 converts the datafrom digital into analog, and outputs a playback audio signal throughthe LPF (low-pass filter) 15 a.

The CLV motor control circuit 11 compares the frequencies and phases ofthe synchronization signal of the CD and the correction framesynchronization signal, extracts error components, and generates a drivesignal of the disc motor 16 to be supplied to the selector 17. To bemore specific, the CLV motor control circuit 11 compares the frequenciesand the phases of the 7.35-XHz CD synchronization signal and the7.35-KHz correction frame synchronization signal.

The CD-ROM signal processing circuit 14 performs detection of CD-ROMsynchronization from CD-ROM data and data descrambling, and executes acorrection process for CD-ROM data and control on writing or reading ofdata into the buffer memory 18. The CD-ROM synchronization signaldetection and the CD-ROM data descrambling are carried out using theclock supplied by the selector 8. Further, the data correction processand the control on the reading or writing of data into the buffer memory18 are executed using the clock supplied by the clock generator 10.Then, the data read from the buffer memory 18 are transferred to a hostcomputer as an external device through the interface control circuit 19.At this time, the writable area in the buffer memory 18 is detected andsupplied to the system controller 6.

The interface control circuit 19 executes a communication controlrelating to interface such as transmission/receipt of an operationcommand and transmission/receipt of data to/from the host computer. Theoperation command is transmitted/received between the system controller6 and the host computer via the interface control circuit 19.

Next, the CAV control circuit 27 generates a drive signal for rotatingthe disc motor 16 at a prescribed rotation conforming to the velocityreference value, from a rpm detection pulse obtained from the disc motor16 and the velocity reference value supplied by the maximum velocitydefinition circuit 22. The generated drive signal is supplied to theselector 17

Further, the CAV control circuit 27 stores the outermost circumferenceradius address on the information disc 2 which has ever been accessed,then in cases where a method for setting this address as the maximumvelocity of the system is adopted, compares the rpm detection pulseobtained from the disc motor 16, with the velocity reference valuesupplied by the maximum velocity definition circuit 22 when theoutermost circumference address value is changed, and supplies a readinhibition signal to the system controller 6 until the disc has avelocity which is equal to or lower than the target velocity.

The switching of the selector 17 is performed in accordance with theaudio/ROM switching instruction signal output by the system controller6. The selector 17 selects the output of the CLV motor control circuit11 when the instruction signal indicates audio, and selects the outputof the CAV control circuit 27 when the signal indicates a CD-ROM, to besupplied to the disc motor 16.

The system controller 6 executes a search or operation control of thewhole CD-ROM such as ON/OFF control of the operation of each circuit.Further, the system controller 6 generates the audio/ROM switchinginstruction signal from sub code data which have been demodulated by theCD signal processing circuit 26, and supplies the instruction signal tothe level slice-PLL circuit 25 and the selectors 8, 12 and 17. Thesearch instructions signal is supplied to the focus-tracking controlcircuit/feed motor control circuit 24.

A method for obtaining the linear velocity and track pitch of theinformation disc in the so-constructed CAV playback system for CD-ROM isdescribed with reference to FIG. 2.

Initially, when the information disc 2 is loaded into the disc playbacksystem, the optical pickup 21 is forcefully transported from the programstart position of the information disc 2 toward the inner radius by onetrack. The optical pickup 21 counts the playback frame synchronizationsignal until it detects the program start position again, whereby thelinear velocity of the information disc 2 can be obtained. There arevarious methods other than this for obtaining the linear velocity of theinformation disc.

Next, to obtain the track pitch of the information disc 2, a method forcompensating the track pitch with respect to the standard maximum value(1.7 μm) with actually playing back data is adopted in this secondembodiment. To be more specific, for example the disc rotation velocitycalculated from the linear velocity of the information disc 2 when theinformation disc 2 is rotated at a prescribed rpm, the innermost radiusof the disc and the standard maximum value of the track pitch (1.7 μm)is used as the initial value of the disc rotation velocity. Then, theplayback velocity at a certain address can be calculated from theinitial value of the rotation velocity and the value of the track pitch.More specifically, the accurate track pitch can be obtained by measuringthe data reading velocity when the data are actually read, thencomparing the data reading velocity with the calculated playbackvelocity, and compensating the track pitch by the addition orsubtraction on the basis of the difference of these velocities. The datareading velocity can be easily obtained, for example, by counting theplayback PLL clock which is output by the level slice-PLL circuit 25,without using special hardware.

The rotation velocity of the information disc 2 is decided using thelinear velocity and track pitch calculated as described above, and acontrol reference value of the rotation velocity of the information disc2 is set in the maximum velocity definition circuit 22.

Next, the method for calculating the rotation velocity of the disc isdescribed in detail.

Initially, the radius position (r_(max)) of the information disc 2 atthe time of the maximum velocity in the disc playback system iscalculated using the following equation:

Equation (1)$\frac{\pi \left( {r_{\max}^{2} - R_{0}^{2}} \right)}{T_{p}} = \frac{V_{i}{AD}_{end}}{{AD}_{unit}}$

$r_{\max} = \sqrt{R_{0}^{2} + \frac{T_{p}V_{1}{AD}_{end}}{\pi \quad {AD}_{unit}}}$

In the above equation, R_(o) is an innermost radius of the record areain the information disc 2 (which is already known from the standards and0.0249±0.002 m in the case of CD-ROM), T_(p) is a track pitch, AD_(unit)is an address value included in a unit time (75 in the case of CD),AD_(end) is an address value of the information disc 2 at the time ofthe maximum velocity, and V₁ is the linear velocity of the informationdisc 2.

For setting the address value AD_(end) on the information disc 2 at thetime of the maximum velocity in the disc playback system, there arefollowing methods. For example, a method of using the standard maximumrecording time, a method of using the maximum time in the data recordarea read from TOC information, or a method of storing the outermostcircumference address on the information disc 2 which has ever beenaccessed and using the stored address as the maximum velocity in thesystem can be used.

Then, the maximum playback velocity rate (DR_(max)) in the system isobtained from the calculated r_(max) using the following equation, andfurther the rotation velocity V_(rpm) of the information disc 2 isobtained from values of r_(max) and DR_(max).

Equation (2)${DR}_{\max} = {\frac{2\pi \quad r_{\max}}{V_{1}}\frac{V_{rpm}}{60}}$

$V_{rpm} = \frac{60{DR}_{\max}V_{1}}{2\pi \quad r_{\max}}$

Here, the value of V_(rpm) is set so as not exceed the upper limit ofthe value which is normally restricted in the mechanism.

Next, an example of the practical calculation of the rotation velocityof the information disc 2 is described.

For example, when the address value at the maximum velocity is assumedthat AD_(end)=60:00:00(=3600 s), the linear velocity of the informationdisc 2 is assumed that V₁=1.3 m/s, the maximum velocity of the system isassumed that DR_(max)32× velocity, the rotation velocity is calculatedin this way.

Initially, the radius position r_(max) at 60:00:00 is calculated usingthe value of 1.6 μm as the standard track pitch in accordance with theEquation (1):

r _(max)=(0.0249²+1.6×10⁻⁶×1.3×3600/π)^(½)=0.0548 m

Then, when the obtained value of r_(max) is substituted into Equation(2), the rotation velocity of the information disc 2 is:

V_(rpm)=(60×32×1.3)/(2π×0.0548)=7249 rpm

When the actual track pitch is 1.5 μm as the standard minimum value, theradius position r_(max) is obtained in accordance with Equation (1).

r _(max)=(0.0249²+1.5×10⁻⁶×1.3×3600/π)^(½)=0.0534 m

When the obtained value of r_(max) is substituted into Equation (2), therotation velocity of the information disc 2 is:

V_(rpm)=(60×32×1.3)/(2π×0.0534)=7439 rpm

Further, when the actual track pitch is 1.7 μm as the standard maximumvalue, the radium position r_(max) is obtained in accordance withEquation (1).

r _(max)=(0.0249²+1.7×10⁻⁶×1.3×3600/π)^(½)=0.0561 m

Then, the obtained value of r_(max) is substituted into Equation (2),the rotation velocity of the Information disc 2 is:

V_(rpm)=(60×32×1.3)/(2π×0.561)=7081 rpm

In this embodiment, since the value of the track pitch is unknown atfirst, it is required to set the maximum velocity by using the standardmaximum value of the track pitch, i.e., 1.7 μm, so as not to exceed thecapability of the system. Further, from the above calculation example,in a case where the track pitch is set at 1.7 μm and the rotationvelocity is set at 7081 rpm, the playback velocity at 60:00:00 is 31.25×(31.25 times faster) velocity when the actual track pitch is 1.6 μm, and30.46× velocity when the actual track pitch is 1.5 μm, whereby themaximum playback velocity is reduced about 5% at the maximum.

Next, the information disc is played back, and when the halfway addressis AD_(end)=20:00:00 (=1200 s) and the track pitch is 1.7 μm, the radiusposition r_(max) at this address is 0.0383 m in accordance with Equation(1), and the rotation velocity of the disc is 7081 rpm in accordancewith Equation (2). Then, the playback velocity at this time is obtainedfrom the following Equation which is obtained by deforming Equation (2).

Equation (3)${DR}_{\max} = {\frac{2\pi \quad r_{\max}}{60V_{1}}V_{rpm}}$

When the above numeric values are substituted into Equation (3), thecalculative playback velocity is:

DR _(max)=2π×0.0383×7081/(60×1.3)=21.8×velocity

When the actual playback velocity is, for example, 21.1× velocity, theactual track pitch can be calculated as follows. Initially, the actualradius position is obtained in accordance with the following equationwhich is obtained by deforming Equation (2).

Equation (4)$r_{\max} = \frac{60{DR}_{\max}V_{1}}{2\pi \quad V_{rpm}}$

From this equation,

r_(max)=(60×21.1×1.3)/(2π×7081)=0.0370 m

Then, the track pitch is obtained in accordance with the followingequation which is obtained by deforming Equation (1).

Equation (5)$T_{p} = \frac{{\pi \left( {r_{\max}^{2} - R_{0}^{2}} \right)}{AD}_{unit}}{V_{1}{AD}_{end}}$

When using Equation (5),

Tp=π(0.0370²−0.0249²)/(1.3×1200)=1.51 μm

However, when the readout address is near the position of the innerradius, there is a possibility that the calculated value of the trackpitch has a large error. Therefore, when the reference value of thevelocity control of the disc motor 16 is decided on the basis of thistrack pitch value, there is a risk that the rotation velocity of theinformation disc 2 exceeds the maximum velocity in the system whenreading data in the position of the outermost circumference radius.Thus, it is preferable to obtain the value of the rotation velocity ofthe information disc 2 with making a compensation by using a valueobtained by multiplying the difference between the theoreticallycalculated track pitch and the track pitch of the information disc 2which is being played back now by a predetermined compensationcoefficient, as a compensation value for the actual track pitch. To bemore specific, for example, when the track pitch obtained at the firstaccess is 1.51 μm and the track pitch used for setting the rotationvelocity of the disc motor 16 is 1.7 μm, the rotation velocity of theinformation disc 2 is re-decided using a value which is obtained bymaking compensation with half of the difference between these trackpitches, i.e., Tp=1.605 μm. That is, from Equations (1) and (2), therotation velocity is:

r _(max)=(0.0249²+1.605×10⁻⁶×1.3×3600/π)^(½)=0.0549 m

 V_(rpm)=(60×32×1.3)/(2π×0.549)=7236 rpm

Hereinafter, by making compensation with half of the difference betweenthe track pitches at each access, the obtained value is graduallyconverging to the true value of the track pitch.

Or, another method is adopted for making compensation by weighting acompensation coefficient according to a distance from the address atwhich the maximum velocity is obtained, in view of the fact that themaximum playback velocity can be set more accurately at a position onthe information disc 2 nearer to the address at which the set maximumvelocity is obtained. To be more specific, for example, the compensationcoefficient at the address where the maximum velocity is obtained is setat 100%, the compensation coefficient is set at 0˜100% according to theaddress position, and then the compensation is made by multiplying thecompensation value of the calculated track pitch, by the compensationcoefficient. In the above-mentioned embodiment, since the address atwhich the maximum velocity is obtained is 60:00:00 and the address atwhich the reading of data has been performed is 20:00:00, thecompensation is made with 33.33% of the difference between the trackpitch values at that time, i.e., 1.7 μm and 1.51 μm.

Tp=1.7+(1.51−1.7)×0.3333=1.637 μm

Then, by using the value of Tp, the rotation velocity of the informationdisc 2 is compensated using Equations (1) and (2).

 r _(max)=(0.0249²+1.637×10⁻⁶×1.3×3600/π)^(½)=0.05353 m

V_(rpm)=(60×32×1.3)/(2π×0.0663)=7184 rpm

Also in this method, when the compensation is made at every access, thevalue is gradually converging to the true track value and further whenthe access is made to a position nearer the address of the maximumvelocity in the system which is supposed to be more accurate, themaximum playback velocity of the system can be attained earlier.

There are various track pitch compensation methods other than these,while when the compensation is made so that the data playback velocityat the address of the maximum velocity of the system on the informationdisc 2 becomes closer to the maximum velocity of the system, the sameeffects are obtained.

On the other hand, the prescribed amount of error is permitted also inthe innermost radius of the information disc 2. When comparing theplayback velocities at the address of 60:00:00, for example, in a casewhere the minimum radius is 0.0247 m and in a case where the maximumradius is 0.0251 m, the radius position when the rpm of the informationdisc 2 is 7081 rpm and the track pitch is 1.7 μm in the case of theminimum radius is obtained from Equation (1).

r _(max)=(0.0249²+1.7×10⁻⁶×1.3×3600/π)^(½)=0.05605 m

Then, from Equation (3),

DR _(max)=(2π×0.05605×7081)/(60×1.3)=31.97×velocity

In the case of the maximum radius, from Equation (1),

 r _(max)=(0.0251²+1.7×10⁻⁶×1.3×3600/π)^(½)=0.05624 m

Then, from Equation (3),

DR _(max)=(2π×0.05624×7081)/(60×1.3)=32.08×velocity

The difference of the playback velocities is approximately 0.35% at themaximum and it is a negligible range of error.

Even it the initially measured linear velocity or innermost radius ofthe information disc 2 has an error, because the actual data readingvelocity is measured, the rotation velocity of the information disc 2can finally be the maximum velocity of the system at the outermostcircumference position in the data area.

In this second embodiment, the value of the track pitch is compensated.However, the same effects are obtained when the compensation is made bycalculating the required rotation velocity of the disc directly from theaddress and playback velocity at which the playback is now beingperformed. In addition, also when the above value is multiplied by thecompensation coefficient, the same effects are obtained.

When the accurate track pitch can be measured by the track pitchmeasuring means shown in the first embodiment at the loading of theinformation disc 2, the rotation velocity of the information disc 2 canbe set by using the measured track pitch from the beginning. Inaddition, in order to set the rotation velocity of the disc moreaccurately, the above-mentioned method for compensating the rotationvelocity of the disc on the basis of the address value and playbackvelocity at which the playback is being performed can be combined.

As described above, the disc playback system according to the secondembodiment comprises the linear velocity detection means for detectingthe linear velocity of the information disc 2 and the playback velocitydetection means for detecting the current playback velocity of theinformation disc 2, and previously decides an initial value of theplayback velocity on the basis of the detected linear velocity value,the standard maximum value of the track pitch and the value of themaximum radius of the data storage area in which data are recorded onthe information disc, measures the playback velocity of data each timewhen the data on the information disc 2 are read out, and decides thereference value of the velocity control of the disc motor 16 on thebasis of the current rotation velocity, linear velocity and innermostradius in the data record area on the information disc 2, the addressvalue at the maximum playback velocity in the system and the addressvalue on the information disc at the maximum velocity. Therefore, nospecial means for detecting the track pitch is required, and the valueof the maximum radius of the data record area in which data are recordedon the information disc 2 can be calculated more inexpensively and moreaccurately, regardless of the values of the linear velocity and thetrack pitch of the information disc 2. In addition, even when thepreviously measured linear velocity of the information disc 2 has anerror, the high-speed search and high-speed reading can be adaptivelyperformed according to the outermost circumference radius of the datarecord area.

Further, since the compensation is made by multiplying, the compensationcoefficient corresponding to the ratio between the address for obtainingthe maximum velocity of the system, and the address at which theplayback is being performed, when the track pitch value is compensatedby multiplying the track pitch value by the compensation coefficientcorresponding to the radius position at which the playback is beingperformed or its address value, the address value of the maximum radiusof the data record area in which data are recorded on the informationdisc can be calculated more accurately, regardless of the radiusposition at which the playback is being performed or its address value,or the values of the linear velocity or track pitch of the disc.Therefore, even when the previously measured linear velocity of the dischas an error, the high-speed search and high-speed reading can beadaptively performed according to the outermost circumference radius ofthe data record area.

Embodiment 3

Hereinafter, the third embodiment of the present invention correspondingto Claims 5 and 6 will be described.

Initially, the maximum radius value of the data record area described inthe first or second embodiment can be obtained by following methods.

For example, there is a method for extracting address informationrecorded on the information disc by means of a pickup, and using theradius at the outermost circumference position obtained from theextracted address information as the maximum radius of the data storagearea.

In addition, there is a method for providing a storage means for storingthe address information at the outermost circumference read at each timewhen the information disc is played back on the information disc, andusing the data record area at the outermost circumference from thestorage means as the maximum radius.

Further, there is a method for using the standard maximum record time asthe maximum radius of the data record area, and a method for reading themaximum time in the data record area in which data are recorded on theinformation disc and using the same as the maximum radius of the datarecord area, and the like.

As described above, in the disc playback system according to the thirdembodiment, the outermost circumference position of the information discor the radius at the outermost circumference address position read fromthe storage means is used as the maximum radius of the data storagearea. Therefore, the outermost circumference radius of the addresseswhich have ever been accessed on the information disc can be calculatedmore accurately regardless of the values of the linear velocity or trackpitch of the information disc, and the high-speed search and thehigh-speed reading can be adaptively carried out according to theaddress value of the outermost circumference radius on the informationdisc which has ever been accessed.

Embodiment 4

Hereinafter, the fourth embodiment of the present inventioncorresponding to Claims 7 to 9 will be described with reference to FIG.2.

FIG. 2 is a block diagram illustrating a disc playback system which isapplied to a CAV playback system for CD-ROM, according to the fourthembodiment. The same reference numerals as those in the secondembodiment denote the same or corresponding elements or operations, anddescriptions thereof are not given here.

In this figure, the information disc 2 on which data are recorded atconstant linear velocity (CLV) is played back by rotating the disc motor16 by the CAV method or CLV method. At this time, the switching betweenthe CAV method and the CLV method is performed in accordance with theaudio/ROM switching instruction signal which is output from the systemcontroller 6. In the case of audio, the information disc 2 is playedback by the CLV method and in the case of CD-ROM, the information disc 2is played back by the CAV method. In addition, when the playback isperformed by the CLV method, a variable clock generation circuit whichcan vary the reference value of the velocity control of the disc motor16 is provided.

As described above, according to the disc playback system of the fourthembodiment, the information disc 2 is played back by the CAV method.Therefore, the loads on the disc motor 16 can be reduced, therebyreducing the costs and downsizing, and further the high-speed search canbe performed.

In addition, the information disc 2 is played back by a wide-range CLVmethod having a playback velocity which is equal to that of the CAVmethod. Therefore, the loads to the disc motor 16 can be reduced,thereby reducing the costs and downsizing, and further the high-speedsearch can be performed

Further, the CLV method and the CAV method are provided as the means forplaying back the information disc 2, and the circuit for switching themethods is further included. Therefore, regardless of the value of thetrack pitch, the maximum radius of the data storage area in theinformation disc 2 can be calculated more accurately, and the high-speedsearch and high-speed reading can be performed adaptively according tothe maximum radius of the data storage area.

Industrial Availability

As described above, the disc playback system according to the presentinvention relates to a disc playback system for controlling the discrotation velocity and can obtain the maximum playback velocity in thesystem even in the case of a disc having a different track pitchtherefore, it is extremely useful as the one for realizing an efficientdisc playback system.

What is claimed is:
 1. A disc playback system comprising: a pickup forreading first information data recorded on an information disc on whichdata are recorded at a constant linear velocity, from the informationdisc; a disc motor for rotating the information disc; a digital signalprocessing circuit for digitizing the first information data accordingto a playback format of the information disc; an interface controlcircuit for transmitting second information data which are the datadigitized by the digital signal processing circuit, to an externaldevice; a buffer memory for temporarily containing the secondinformation data which are requested by the external device via theinterface control circuit; a linear velocity detection means fordetecting a linear velocity of the information disc; and a track pitchdetection means for detecting a track pitch of the information disc,said disc playback system deciding a reference value for controlling avelocity of the disc motor, on the basis of the linear velocity detectedby the linear velocity detection means, the track pitch detected by thetrack pitch detection means, and a value of a maximum radius of a recordarea of data which are recorded on the information disc.
 2. The discplayback system of claim 1 wherein the track pitch detection meanscomprises a motion distance detection means for detecting a motiondistance of the pickup, and when the information disc is loaded, themotion distance detection means calculates the number of tracks whichhave been passed by the pickup while the pickup is moving on the datarecord area on the information disc for a prescribed time period or by aprescribed distance, thereby detecting the track pitch of theinformation disc.
 3. The disc playback system of claim 1 extractingaddress information concerning the information disc which is stored in adisc start position, from the first information data, and using a valueof a radius in a maximum circumference position obtained by the addressinformation, as the value of the maximum radius of the record area ofdata which are recorded on the information disc.
 4. The disc playbacksystem of claim 1 comprising a storage means for containing addressinformation of the outermost circumference among already read addressinformation on the information disc, and using a radius of an addressposition of the outermost circumference, read from the storage means, asthe value of the maximum radius of the record area of data which arerecorded on the information disc.
 5. A disc playback system comprising:a pickup for reading first information data recorded on an informationdisc on which data are recorded at a constant linear velocity, from theinformation disc; a disc motor for rotating the information disc; adigital signal processing circuit for digitizing the first informationdata according to a playback format of the information disc; aninterface control circuit for transmitting second information data asdata which have been digitized by the digital signal processing circuit,to an external device; a buffer memory for temporarily containing thesecond information data which are requested by the external device viathe interface control circuit; a linear velocity detection means fordetecting a linear velocity of the information disc; and a playbackvelocity detection means for detecting a playback velocity of theinformation disc during playback of the information, said disc playbacksystem previously deciding an initial value of a reference value forcontrolling a velocity of the disc motor on the basis of the linearvelocity detected by the linear velocity detection means, a standardmaximum value of a track pitch of the information disc, and a value ofthe maximum radius of a record area of data which are recorded on theinformation disc, when data are read from the information disc, settingagain the reference value for controlling the velocity of the disc motoradaptively on the basis of the playback velocity of the information discduring playback, which is detected by the playback velocity detectionmeans, the linear velocity detected by the linear velocity detectionmeans, and a value of an address at which the playback is beingperformed, and deciding thee reference value for controlling thevelocity of the disc motor.
 6. The disc playback system of claim 5wherein the reference value for controlling the velocity of the discmotor is obtained, when the reference value for the velocity control isset again, by making a compensation by multiplying the initial value ofthe motor velocity control reference value, by a compensationcoefficient corresponding to a ratio between a radius position at whichthe information disc is being played back or an address value thereof,and the value of the maximum radius of the data record area or anaddress value thereof.
 7. The disc playback system of claim 6,extracting address information concerning the information disc which isstored in a disc start position, from the first information data, andusing a value of a radius in a maximum circumference position obtainedby the address information, as the value of the maximum radius of therecord area of data which are recorded on the information disc.
 8. Thedisc playback system of claim 6 comprising a storage means forcontaining address information of the outermost circumference amongalready read address information on the information disc, and using aradius of an address position of the outermost circumference, read fromthe storage means, as the value of the maximum radius of the record areaof data which are recorded on the information disc.
 9. The disc playbacksystem of claim 5 extracting address information concerning theinformation disc which is stored in a disc start position, from thefirst information data, and using a value of a radius in a maximumcircumference position obtained by the address information, as the valueof the maximum radius of the record area of data which are recorded onthe information disc.
 10. The disc playback system of claim 5 comprisinga storage means for containing address information of the outermostcircumference among already read address information on the informationdisc, and using a radius of an address position of the outermostcircumference, read from the storage means, as the value of the maximumradius of the record area of data which are recorded on the informationdisc.
 11. The disc playback system of any of claims 1-10 wherein thedisc motor comprises: a CAV (Constant Angular Velocity) control circuitfor rotating the information disc at a constant angular velocity. 12.The disc playback system of any of claims 1-10 wherein the disc motorcomprises: a CLV (Constant Linear Velocity) control circuit for rotatingthe information disc at a constant linear velocity, and a variable clockgeneration circuit which can vary a comparison clock supplied to the CLVcontrol circuit on the basis of the reference value for controlling thevelocity of the disc motor.
 13. The disc playback system of any ofclaims 1-10 wherein the disc motor comprises: a first rotation controlmeans for rotating the information disc at a constant angular velocity,a second rotation control means for rotating the information disc at aconstant linear velocity, and a switch circuit for switching the firstrotation control means and the second rotation control means.